Python interpreter in python?

[Raymond Biurrun]

"Steven D. Majewski" <sdm7g at virginia.edu> escribió en el mensaje
news:mailman.977254923.336.python-list at python.org...
>
> That is absolutely untrue!
>
> Lisp and Scheme are frequently implemented in themselves -- a
> 'metacircular interpreter' is a fairly typical student exercise.
>

Please excuse my ignorance but what's a "metacircular interpreter" and where
can I find info about them.

Regard -- Raymond